For power electronics equipment such as inverters, further energy saving is constantly demanded. For this reason, it is required to reduce the loss of the power semiconductor element used therefor. An insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), a positive intrinsic negative (PiN) diode, a Schottky barrier diode (SBD), and so forth, are particularly required such reduction in loss. As an effective method for reducing the loss, instead of silicon (Si), which is the most common semiconductor material, a method of using silicon carbide (SiC) has been studied; for example, practical application thereof has started in the railway field and so forth. Utilization of the fact that SiC has a higher dielectric breakdown electric field than Si reduces the thickness of the device further, thereby reducing the loss. Furthermore, using SiC ensures the high temperature operation, therefore, it is also useful for downsizing of equipment for cooling a semiconductor element. Therefore, SiC devices are considered to become more popular in the market as their cost reduction progresses.
SiC devices are expected to be used in the breakdown voltage region of several 100 V to several 10 kV. Such a device is typically provided with a terminal structure referred to as a field limiting ring (FLR) or a guard ring to ensure sufficient breakdown voltage.
It is known that some fixed charge may exist at the interface between SiC and an insulator such as silicon dioxide (SiO2). According to Non-Patent Document 1, it is stated that a positive charge of +2.4×1012 cm−2 exists at the interface between the p-type SiC having the plane orientation (0001) and the SiO2 film formed by the dry oxidation. According to Non-Patent Document 2, it is stated that when an oxide film is formed by dry oxidation, a negative charge of −1.4×1012 cm−2 exists at the interface between n-type SiC having plane orientation (0001) and SiO2.
Fixed charge may affect device characteristics. In Patent Document 1, the influence of the positive surface charge between the oxide and the semiconductor is reduced by providing a low-concentration p-type surface-charge compensation region between the p-type guard ring layers. In Patent Document 2, utilizing the factor that a positive fixed charge layer is formed by dry oxidation and the factor that a negative fixed charge layer is formed by wet oxidation and wet reoxidation, with the depletion layer between the SiC and the interface fixed charge layer, thereby obtaining the electric field relaxation effect.